The Western Design Center, Inc.

W65C02S Data Sheet

The Western Design Center, Inc.

W65C02S Data Sheet

10

3.7

No Connect (NC)

The No Connect (NC) pins are not connected internally and should not be connected externally.

3.8

Phase 2 In (PHI2), Phase 2 Out (PHI2O) and Phase 1 Out (PHI1O)

Phase 2 In (PHI2) is the system clock input to the microprocessor internal clock. During the low power Standby

Mode, PHI2 can be held in either high or low state to preserve the contents of internal registers since the

microprocessor is a fully static design. The Phase 2 Out (PHI2O) signal is generated from PHI2. Phase 1 Out

(PHI1O) is the inverted PHI2 signal. An external oscillator is recommended for driving PHI2 and used for the main

system clock. All production test timing is based on PHI2. PHI2O and PHI1O were used in older systems for

system timing and internal oscillators when an external crystal was used.

3.9

Read/Write (RWB)

The Read/Write (RWB) output signal is used to control data transfer. When in the high state, the microprocessor is

reading data from memory or I/O. When in the low state, the Data Bus contains valid data to be written from the

microprocessor and stored at the addressed memory or I/O location. The RWB signal is set to the high impedance

state when Bus Enable (BE) is low.

3.10 Ready (RDY)

A low input logic level on the Ready (RDY) will halt the microprocessor in its current state. Returning RDY to the

high state allows the microprocessor to continue operation following the next PHI2 negative transition. This bi-

directional signal allows the user to single -cycle the microprocessor on all cycles including write cycles. A negative

transition to the low state prior to the falling edge of PHI2 will halt the microprocessor with the output address lines

reflecting the current address being fetched. This assumes the processor setup time is met. This condition will

remain through a subsequent PHI2 in which the ready signal is low. This feature allows microprocessor interfacing

with low-speed memory as well as direct memory access (DMA). The WAI instruction pulls RDY low signaling the

WAit-for-Interrupt condition, thus RDY is a bi-directional pin. On the W65C02 hard core there is a WAIT output

signal that can be used in ASIC's thus removing the bi-directional signal and RDY becomes only the input. In such

a situation the WAI instruction will pull WAIT low and must be used external of the core to pull RDY low or the

processor will continue as if the WAI never happened.

The microprocessor will be released when RDY is high and

a falling edge of PHI2 occurs. This again assumes the processor control setup time is met. The RDY pin has an

active pull-up, when outputting a low level, the pull-up is disabled. The RDY pin can still be wire ORed.